Compute the weight of collpased regions the first time it is requested
and cache it, and use the cached value for all successive queries.
This also prevents a bug which occurs when we query the weight two
times for the same collapsed node, whose related collapsed region object
has been in the meantime destroyed by the tiling process.
Now that the late stage of the decompilation pipeline is managed with
revng-pipeline, and we have a standalone tool for decompilation, we
have no need to use LLVM passes anymore for those stages.
This commit also renames the directories to avoid the confusing Pass
suffix, not what LLVM passes are gone.
Alessandro Di Federico